This invention relates to a packet exchange apparatus. More particularly, it relates to a broad-band optical packet exchange apparatus employing an inexpensive optical/electrical converter.
In a packet exchange apparatus employing an optical switch in an exchange stage and also employing an electrical/optical converter and an optical/electrical converter in an input/output unit, the optical/electrical converter is usually of an ac coupling circuit configuration. In this case, there is presented a problem that, if there is any time period during which the 1 or 0 level continues for a longer time than a pre-set time period or during which there is no packet to be received, data dropout occurs in the packet or in the directly following packet.
As a method for overcoming this problem, there is proposed in, for example, JP Patent Kokai JP-A-4-72939 a packet exchange apparatus employing an optical switch in which a dummy data appending circuit is provided on the transmission side so that dummy data is transmitted during a domain (length of time) in which there is no transmission data while the appended dummy data is removed by a dummy data removing circuit provided on the reception side, so that it is attempted to eliminate occurrence of no time devoid of transmission data on the transmission route there is no continuation of 0 or 1 for a longer time than a pre-set time, thus eliminating the malfunction of data dropout in the optical/electrical converter. This method consists in sending a dummy packet in the absence of packets for transmission on the input side.
This dummy packet is a pattern which is made up of at least one bit of 0 and the same number of bit of 1, with 0 or 1 not continuing for longer than a pre-set time, and to which is appended a particular code by which the packet can be judged to be a dummy packet. An output unit includes a dummy packet eliminating circuit which discriminates a dummy packet based on the possible presence of the particular code specifying a dummy packet to eliminate the discriminated dummy packet in order to receive only the necessary packets.
In case where, in this configuration, there are packets to be transmitted to the same output unit on plural input units, a contention resolution circuit is used in order to inhibit packet interference due to arrival of plural packets at the same output unit, which would lead to reception of erroneous data.
If a connection request is received from the input unit before the input unit sends a transmission packet and connection requests are made to the sole output unit from plural input units, the contention resolution circuit selects a sole input unit from the plural input units to give the input unit a permission for connection. The remaining input units are inhibited from connection. Since the input units inhibited as to connection are equivalent to the input units devoid of the packets for transmission, these input units send dummy packets. The contention resolution circuit has to detect an input unit devoid of the packets for transmission and an output unit devoid of packets for reception and to find out a connection pattern to interconnect these input and output units.
FIG. 37 shows a configuration of a conventional optical switch used in an exchange stage. Referring to FIG. 37, this optical switch is a 4-input 4-output splitter/combiner type optical switch having four light splitters 10, 16 optical gates 11 and four light combiners 12. For controlling this switch, 42 or 16 control lines are required to control the 16 optical gates.
During the course of investigations toward the present invention, the following problems have been encountered.
In sending packets from a sending station to the exchange apparatus, the sending station transmits, along with a packet(s), a destination address specifying the receiving station to receive the packet(s), to the exchange apparatus. In the absence of packets to be transmitted in the input unit, no designation of the destination address is made from the transmitting station to the input unit.
In transmitting a dummy packet by the above-described conventional packet exchange apparatus, a contention resolution circuit searches an input unit devoid of a packet(s) to be transmitted and an output unit devoid of a packet(s) to be received and controls the optical switch driving circuit for interconnecting these input and output units.
Unless this search is expedited or it is constructed so as to unnecessitate the search, the exchange apparatus is increased in the circuit scale. If the network speed is increased, it becomes impossible to control the exchange apparatus at a high speed.
Meanwhile, since the dummy packet is deemed in the receiving station as being unnecessary or erroneous data, it is necessary to provide a dummy packet eliminating system in order to prevent the dummy packet from being output from the exchange apparatus to the receiving station.
In the dummy packet eliminating system of the conventional packet exchange apparatus, described above, the special code specifying a dummy packet appended to the dummy packet is detected for eliminating the dummy packet. That is, in case where a packet other than the dummy packet is received as a substitute for the dummy packet in order to avoid mulfunction of an O/E converter of an output unit inherently having no packet to be received, the dummy packet eliminating system cannot eliminate this packet as an invalid packet and erroneously sends this packet to the reception station.
Therefore, in the above-described conventional packet exchange apparatus, an output unit devoid of the packet to be received has to be connected to an input unit transmitting a dummy packet, that is to an input unit devoid of the packet to be transmitted, such that it becomes necessary to search and connect input and output units sending and receiving the dummy packet expeditiously.
Another problem is the interconnection for control signals for the optical switch. That is, if the optical switch is increased in scale, the control signal lines between the optical switch and the control circuits are increased in volume and structure thus causing congestion of the control signal lines.
For example, if, in the case of a 128 by 128 line full-cross bus switch, a bit map of the switch connection pattern is formulated in the control circuit and a control signal is sent to the optical switch, 1282 or 16384 control lines are required. Since these numerous control signal lines affect mounting of the exchange apparatus or optical switches, it is incumbent to reduce the- number of the control signal lines.
In view of the above-described problems, it is a primary object of the present invention to eliminate any of the aforementioned problems. Particularly, it is an object of the present invention to provide an optical packet exchange apparatus and an optical switch in which searching for connection patterns between input units devoid of packet(s) for transmission and output units devoid of packet(s) for reception is reduced and can be performed speedily. It is another object to provide an optical packet exchange apparatus and an optical switch in which, if the number of channels of the exchange apparatus is increased or the network speed is higher, switch control can be made quickly to suppress or reduce the hardware scale.
Still further objects of the present invention will become apparent in the entire disclosure including the claims.
For accomplishing the above object, the first aspect of the present invention resides in the following features: An optical packet exchange apparatus includes (a) a plurality of input devices having input buffer means (units), parallel/serial conversion means (units), electrical/optical conversion means (units), and dummy packet insertion means (units) for sending a dummy packet if there is no packet to be transmitted. The apparatus further includes (b) exchange counterpart contention resolution means (units) for controlling an exchange counterpart, (c) a plurality of output devices having optical/electrical conversion means (units), serial/parallel conversion means (units) and packet eliminating means (units), and (d) an optical switch (e) wherein the packets are exchanged, and (f) wherein the exchange counterpart contention resolution means (units) controls the packet eliminating means to eliminate the dummy packet.
In a second aspect of the present invention, related to the first aspect of the invention, the packet exchange apparatus is characterized in that the dummy packet inserting means includes a dummy packet generating circuit, a selector circuit and a packet readout circuit for controlling the selector circuit and the input buffer means.
In a third aspect of the present invention, related to the first aspect of the invention, the packet exchange apparatus is characterized in that the dummy packet inserting means is an encoding circuit and the dummy packet eliminating means is a decoding circuit.
In a fourth aspect of the present invention, a packet exchange apparatus includes (a) a plurality of input devices having input buffer means, parallel/serial conversion means and electrical/optical conversion means, (b) a dummy packet inputting device for transmitting a dummy packet, (c) exchange counterpart contention resolution means for controlling an exchange counterpart, (d) a plurality of output devices having optical/electrical conversion means, serial/parallel conversion means and packet eliminating means, and (e) an optical switch; and (f) the exchange counterpart contention resolution means controls the packet eliminating means to eliminate the dummy packet.
In a fifth aspect of the present invention, a packet exchange apparatus includes (a) a plurality of input devices having input means, parallel/serial conversion means, electrical/optical conversion means, and dummy packet insertion means for sending a dummy packet if there is no packet to be transmitted, (b) exchange counterpart contention resolution means for controlling an exchange counterpart, (c) a plurality of output devices having optical/electrical conversion means, serial/parallel conversion means and packet eliminating means, and (d) an optical switch. (e) The output device includes an address comparator circuit for controlling the packet eliminating means based on results of comparison of the destination address of the received packet to an address allocated to the output device.
In the sixth aspect of the present invention, related to the fifth aspect of the invention, the dummy packet inserting means (unit) includes a dummy packet generating circuit, a selector circuit and a packet readout circuit for controlling the selector circuit and the input buffer means.
In the seventh aspect of the present invention, related to the fifth aspect of the invention, dummy packet inserting means is an encoding circuit and the dummy packet eliminating means is a decoding circuit.
In the eighth aspect of the present invention, related to the fifth aspect of the invention, the destination address in the dummy packet is set to an address other than the address allocated to the connected output device.
In a ninth aspect of the present invention, a packet exchange apparatus includes (a) a plurality of input devices having input buffer means, parallel/serial conversion means and electrical/optical conversion means; (b) a dummy packet inputting device for transmitting a dummy packet; (c) exchange counterpart contention resolution means for controlling an exchange counterpart; (d) a plurality of output devices having optical/electrical conversion means, serial/parallel conversion means and packet eliminating means; and (e) an optical switch. (f) The output device includes an address comparison circuit which controls the packet eliminating means from the results of comparison of a destination address of a received packet to an address allocated to the output device.
In a tenth aspect of the present invention, related to the ninth aspect of the invention, the destination address in the dummy packet is set to an address other than the address allocated to the connected output device.
In a eleventh aspect of the present invention, a packet exchange apparatus includes (a) a plurality of input devices having input buffer means, parallel/serial conversion means, electrical/optical conversion means, and dummy packet insertion means for sending a dummy packet if there is no packet to be transmitted; (b) exchange counterpart contention resolution means for controlling an exchange counterpart; (c) a plurality of output devices having optical/electrical conversion means, serial/parallel conversion means, packet eliminating means and dummy packet code detection means for detecting a code specifying a dummy packet to control the packet eliminating means; and (d) an optical switch. It is characterized by further including (e) a dummy packet destination address calculating circuit setting a connection pattern so that different input devices output dummy packets to respective non-selected output devices.
In a twelfth aspect of the present invention, related to the eleventh aspect of the invention, dummy packet inserting means includes a dummy packet generating circuit, a selector circuit and a packet readout circuit controlling the selector circuit and the input buffer means.
In a thirteenth aspect of the present invention, related to the eleventh aspect of the invention, dummy packet inserting means is an encoding circuit and the dummy packet eliminating means is a decoding circuit.
In a fourteenth aspect of the present invention, an optical packet exchange apparatus includes (a) a plurality of input devices having input buffer means, parallel/serial conversion means, electrical/optical conversion means and dummy packet insertion means for sending a dummy packet if there is no packet to be transmitted; (b) exchange counterpart contention resolution means for controlling an exchange counterpart; (c) a plurality of output devices having optical/electrical conversion means, serial/parallel conversion means, packet eliminating means and dummy packet code detection means for detecting a code specifying a dummy packet to control the packet eliminating means; (d) an optical switch. It is characterized by further including (e) a dummy packet sender addresses calculating circuit for setting a connection pattern so that a non-selected output device (unit) will receive a dummy packet from at least one input device (unit) having no packet to be transmitted.
In a fifteenth aspect of the invention, dummy packet inserting means includes a dummy packet generating circuit, a selector circuit and a packet readout circuit controlling the selector circuit and the input buffer means.
In a sixteenth aspect of the invention, dummy packet inserting means is an encoding circuit and the dummy packet eliminating means is a decoding circuit.
In a seventeenth aspect of the invention, an optical packet exchange apparatus includes:
(a) a plurality of input devices having input buffer means, parallel/serial conversion means and electrical/optical conversion means; (b) a dummy packet input device transmitting a dummy packet; (c) exchange counterpart contention resolution means for controlling an exchange counterpart; (d) a plurality of output devices having optical/electrical conversion means, serial/parallel conversion means and packet eliminating means; and (e) an optical switch, (f) wherein the output device includes a dummy packet code detection circuit detecting a code specifying a dummy packet, for controlling the packet eliminating means, and (g) wherein an output device having no packet to be received is connected to the dummy packet input device.
In an eighteenth aspect of the invention, an optical switch includes (a) a plurality of transmitters having variable wavelength electrical/optical converting means and address decoding means; (b) optical combining/splitting means; and (c) a plurality of receivers (reception devices) having fixed wavelength filter means and optical/electrical converting means, and is characterized by further including (d) an address conversion circuit converting an address to be accorded to the address decoding means from a sender address for a receiver to a destination address for a transmitter (sender device).
In a nineteenth aspect of the invention, an optical switch includes (a) a plurality of transmitters having fixed wavelength electrical/optical conversion means having different wavelengths allocated to different transmitters; (b) optical combining/splitting means; (c) a plurality of receivers having wavelength selection means, optical/electrical converting means and address decoding means; and further including (d) an address conversion circuit converting an address to be accorded to the address decoding means from a destination address for a transmitter to a sender address for a receiver.
In a twentieth aspect oft the invention, an optical switch includes (a) M groups of variable wavelength electrical/optical converting means, each of the groups having N variable wavelength electrical/optical converting means each outputting an optical signal of any one of M different wavelengths xcex1, xcex2, . . . xcexM, N and M being integers not less than 2; (b) Mxe2x80x94number of Nxc3x97Kxe2x80x94optical spatial switch means for switching paths of N optical output signals of one group of the variable wavelength electrical/optical converting means, K being an integer not less than 2; (c) Kxe2x80x94number of optical combining/splitting means for combining optical signals from respective different output ports of the Mxe2x80x94number of Nxc3x97Kxe2x80x94optical spatial switch means for splitting the combined signal into Mxe2x80x94number of outputs; (d) MKxe2x80x94number of fixed wavelength filter means; and (e) MKxe2x80x94number of optical/electrical converting means. (f) The optical spatial switch includes (f1) Nxe2x80x94number of optical splitting means branched into K branches, (f2) optical gate means for turning optical signals branched by the optical splitting means on/ off, and (f3) Kxe2x80x94number of optical combining means for combining optical signals from Kxe2x80x94number of different optical branching means. The optical switch further includes address decoding means for controlling the variable wavelength electrical/optical converting means and one of the optical gate means connected to the optical splitting means.
In a twenty-first aspect of the invention, related to the twentieth aspect of the invention, address conversion means for converting a sender address for a receiver to a destination address for a transmitter to enter the converted destination address to the address decoding means.
In a twenty-second aspect of the invention, an optical switch includes; (a) K groups of fixed wavelength electrical/optical converting means, each of the groups having Mxe2x80x94number of fixed wavelength electrical/optical converting means to which are allocated M different wavelengths xcex1, xcex2, . . . , xcexM, M and K being integers not less than 2; (b) Kxe2x80x94number of optical combining/splitting means for combining Mxe2x80x94number of optical outputs of one group of the fixed wavelength electrical/optical converting means and for branching the combining signal into M branches; (c) Mxe2x80x94number of Kxc3x97N optical spatial switch means having outputs of K different optical combining/splitting means as inputs, N being an integer not less than 2; (d) MNxe2x80x94number of wavelength selecting means for selecting an optical signal of any wavelength from the outputs of the optical spatial switch means, to output the selected signal; and (e) MNxe2x80x94number of optical/electrical converting means. (f) The optical spatial switch means has (f1) Kxe2x80x94number of optical splitting means branched into N branches, (f2) optical gate means for turning the optical signals branched by the optical splitting means on/off, and (f3) Nxe2x80x94number of optical combining means for combining optical signals branched by the K different optical branching means. (g) There is further provided address decoding means for controlling one of the optical gate means connected to the optical combining means and the wavelength selecting means by a sender address for a receiver.
In a twenty-third aspect of the invention, related to the twenty-second aspect, there is address conversion means for converting a destination address for a transmitter to a sender address for a receiver to supply the converted destination address to the address decoding means.
In the optical packet exchange apparatus according to the 24th aspect, related to the first aspect, (bx) the exchange counterpart contention resolution means:
(b1) judges contention on respective output devices based on a destination address from the input device and connection request signals, (b2) sets a connection pattern of the optical switch from the results of contention judgment, and (b3) sets a connection pattern so that an output device not required to be connected is connected to one of the input devices, (dx) wherein optical switch control means controls the optical switch to connect the input and output devices in accordance with the connection pattern, and, (by) wherein said exchange counterpart contention resolution means sends a packet discarding control signal to the packet eliminating means of the output device not required to be connected to eliminate a dummy packet.